However, it's important to note that even if you add up the percentage risk of all of these factors, they only account for about 35% of the overall risk of getting dementia. This means about 65% of the risk is still due to factors you can't control, such as ageing and family history.
Although not guaranteed to prevent dementia, acting on the risk factors above should improve your physical and mental wellbeing.

What is dementia?

Dementia refers to a group of symptoms associated with the gradual decline of the brain and its abilities. Symptoms include problems with memory loss, language and thinking speed.
The most common cause of dementia is Alzheimer's disease. Vascular dementia is the next most common, followed by dementia with Lewy bodies.
For more information, visit the NHS Choices Dementia Guide.

Where did the review come from?

This review was written by the Lancet Commission on Dementia Prevention, Intervention and Care (LCDPIC). The commission is established by convening experts in the field to consolidate current and emerging evidence on preventing and managing dementia. It generates evidence-based recommendations on how to address risk factors and dementia symptoms. These are presented in this review.
The LCDPIC endeavoured to use the best possible evidence to make the recommendations. However, in cases where the evidence was incomplete, it summarised the balance of the evidence, drawing attention to the strengths and limitations.
The media in general has covered the review responsibly and accurately, with helpful comments from experts in the field.

What does the review say?

The review examines aspects of how better to manage the burden of dementia: the risk factors, interventions for prevention and interventions for treatment.

Risk factors

The LCDPIC discusses the effects of several different risk factors potentially linked to dementia.
The review reported population attributable fractions (PAFs). PAFs are an estimate of the proportion of cases of a certain outcome (in this case, dementia) that could be avoided if exposure to specific risk factors were eliminated – for example, how many lung cancer cases would be prevented if nobody smoked.
Using the available evidence, researchers calculated PAFs for the following risk factors.

Education

Less time in education – specifically, no secondary school education – was responsible for 7.5% of the risk of developing dementia.

Hearing loss

The relationship between hearing loss and the onset of dementia is fairly new. It's thought that hearing loss may add stress to an already vulnerable brain with regard to the changes that occur. Hearing loss may also increase feelings of social isolation. However, it's also possible that old age could have a role to play in this association.
The LCDPIC analysis found that hearing loss could be responsible for 9.1% of the risk of developing dementia.

Exercise and physical activity

A lack of physical activity was shown to be responsible for 2.6% of the risk of dementia onset. Older adults who do not exercise are less likely to maintain higher levels of cognition than those who do engage in physical activity.

Hypertension, type 2 diabetes and obesity

These three risk factors are somewhat interlinked; however, all had PAFs lower than 5%, with hypertension contributing the greatest risk of the three:

hypertension – 2%

type 2 diabetes – 1.2%

obesity – 0.8%

Smoking

Smoking was found to contribute to 5.5% of the risk of dementia onset. This is a combination of smoking being more widespread in older generations, and there being a link between smoking and cardiovascular conditions.

Depression

It's possible that depressive symptoms increase dementia risk due to their effect on stress hormones and hippocampal volume. However, it's not clear whether depression is a cause or a symptom of dementia. It was found to be responsible for 4% of the risk of developing dementia.

Lack of social contact

Social isolation is increasingly thought to be a risk factor for dementia as it also increases the risk of hypertension, heart conditions and depression. However, as with depression, it remains unclear whether social isolation is a result of the development of dementia.
It was found to contribute to 2.3% of the risk of developing dementia.

Prevention of dementia

The review highlights that although there are potentially modifiable risk factors for dementia, this does not mean dementia as a condition is preventable or easy to treat. It is evident that there are multiple risk factors contributing to the onset of the disease. However, some interventions that could prevent onset include:

Using antihypertensive drugs, such as ACE inhibitors, in people with hypertension.

Encouraging people to switch to a Mediterranean diet, which is largely based on vegetables, fruit, nuts, beans, cereal grains, olive oil and fish. This has been proven to improve cardiovascular health, and may help with the symptoms of type 2 diabetes, obesity and hypertension.

Encouraging people to meet the recommended physical activity levels for adults. Again, regular exercise may help with the symptoms of type 2 diabetes, obesity and hypertension.

Using cognitive interventions, such as cognitive training, which involves a series of tests and tasks to improve memory, attention and reasoning skills. The review points out, however, that the clinical effectiveness of most commercially available brain-training tools and apps is unproven.

Encouraging people to become more socially active. This could be by organising social activities – book clubs, for example – for older adults.